Apparatus for coating articles in a fluidized bed



y 25, 1965 c. E. MANNING 3,185,131

APPARATUS FOR COATING ARTICLES IN A FLUIDIZED BED Filed Oct. 24. 1960 3 Sheets-Sheet l IN VEN TOR.

GRNEY May 25, 1965 c. E. MANNING APPARATUS FOR COATING ARTICLES IN A FLUIDIZED BED Filed Oct. 24, 1960 3 Sheets-Sheet 2 HAHLES f. MANNING 1s Armm vev y 25, 1965 c. E. MANNING 3,185,131

APPARATUS FOR COATING ARTICLES IN A FLUIDIZED BED Filed Oct. 24, 1960 3 Sheets-Sheet 3 INVENTOR. CHARLES E. MANNING HIS ATTORNEY United States Patent 3,185,131 APPARATUS FOR COATING ARTICLES 1N A FLUIDIZED BED Charles E. Manning, Warren, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Oct. 24, 1960, Ser. No. 64,324 2 Claims. (Cl. 118-421) This invention relates to an apparatus for coatitng articles uniformly with a plastic coating.

It is the main object of this invention to provide an apparatus for uniformly coating articles in a fluidized bed of plastic particles.

In carrying out the above object it is a further object to provide an apparatus for suspending plastic particles in a cloud and to then cause said cloud to rise into contact with a heated article for depositing particles uniformly thereon and then to retract the cloud of suspended particles away from the article leaving the article with a uniform coating of platsic powder adhered thereto,

A still further object of the invention is to provide an apparatus for coating the surface of an electrical stator having coil winding slots therein wherein the heated stator is positioned immovable in a horizontal position in a fixture. A fluidized cloud of plastic particles is then moved thereover to completely envelope the stator and to cause deposition and adherence of the plastic particles in the cloud all over the vertical and horizontal surfaces of the stator in a substantially uniform thickness and to thereafter retract the cloud of fluidized material and to remove the coated stator from the fixture whereupon homogeneity of the coating may be improved by subsequently heating the stator at a temperature above the melting point of the plastic.

Another object of this invention is to maintain the density of the fluidized bed substantially constant from one operation to the next for improving the uniformity of the coating operation.

Further objects and advantages may be apparent, reference being had to the accompanying drawing wherein a preferred form of embodiment is shown.

In the drawings:

FIG. 1 is a view of the apparatus used for coating a stator in the open condition.

FIG. 2 shows the apparatus of FIG. 1 in the closed position with the internal mask expanded within the stator.

FIG. 3 is a section taken of line 33 of FIG. 2 showing the blow off jets.

FIG. 4 is a section taken on line 4-4- of FIG. 2 showing the mask in relation to the stator.

In FIG. 5 is a view of the apparatus shown in FIG. 2 wherein the fluidized chamber has been constricted, or reduced in volume to cause the cloud of fluidized plastic particles to rise through the stator in the direction indicated and to the level noted by the arrows.

Fluidized coatitngs of various plastic powders such as polyethylene, epoxies, polystyrene and other plastic materials are well known in the art wherein the powder in finely divided form is placed in a tank or bed having a foraminiferous bottom, the porosity of the bottom being insufficient to permit the powder to pass therethrough. When it is desired to fluidize the powder, a blast of air or gas in controlled quantities is supplied to the chamber beneath the foraminiferous bottom thereof which causes the plastic powder to rise within the chamber in the form of a suspended cloud of particles. This cloud takes on the appearance of a boiling liquid and the density thereof and the distance of the rise of the cloud may be accurately controlled by the quantity of plastic 3,185,13l Patented May 25, 1965 particles initially placed in the chamber and the quantity and velocity of air or other gas which is passed therethrough. After the cloud is established the article to be coated which has previously been heated to a temperature slightly in excess of the melting point of the particular plastic powder being used is immersed in the fluidized bed of plastic particles. This takes but a short period of time whereupon the article is removed from the fluidized bed and is found to have a coating all over the surface thereof of adhered plastic particles. It is preferable in most cases to subsequently heat the article slightly above the melting point of plastic powder to consolidate the coating. Operations of this general character are described in some detail in Gemmer Patent No. 2,884,489, wherein satisfactory plastic powders, temperatures and times for useful deposition and the control factors are set forth.

in the coating of articles having restircted vertical passages considerable difiiculty has been experienced in obtaining a uniform coating along the walls of the vertical passages and particularly to obtain a uniform coating at the edge portions of the vertical passages. One such article is a motor stator having coil slots preferably disposed therearound and opening into a central bore through reduced area portions. It has been found that when coating such an article in a fluidized bed that the edges of the coil slots have a thinner coating and that the horizontal surfaces have a greater coating of plastic than do the verticals whereby the uniformity of coating is diflicult to maintain.

Various expedients are used to form a uniform coating for this type of article and one of such as described in the aforesaid patent wherein the article is vibrated to reduce the thickness of the coating on the horizontal surfaces. The present invention is directed to an apparatus and method for uniformly coating such articles and, for that matter any other article wherein the article is not vibrated but is maintained stationary at all times and wherein a uniform coating is obtained by a close control of the fluidized bed envelopment of the article.

The apparatus used to perform the method is shown in FIGS. 1 through 5 wherein a vertical stand is provided which supports an upper plate 22 thereon which is vertically movable by means of a column 24 attached to suitable hydraulic means. The plate 22 carries an upper chamber 26 formed by an annular wall 28 which is at tached to the plate 22. A lower chamber 30 is also provided formed by an annular wall 32 attached to the stand 20 through plate 21. The stator 34 to be coated is set upon the annular housing 32 in a heated condition as shown in FIG. 1 and the column 24 is actuated to move the plate 22 and its open chamber 26 downwardly toward the stator.

Mounted concentrically within the chamber 26 is a resilient inflatable mask 36 preferably formed from butyl rubber which is carried by plate 40 attached to the upper end thereof and is plugged by means of plug 42 in the lower end thereof. Plate 40 is apertured to permit passage of tubes 4-4 and 46 which are inlet and outlet tubes for Water or other fluid which is used as a hydraulic medium in the mask.

As the upper plate 22 descends the mask 36 in deflated condition passes through the central aperture 59 of the stator 34. The limit of downward movement is de termined by abutment of the annular housing 28 with the upper surface of the stator 34 as noted in FIG. 2. When this position is reached water or other hydraulic medium is passed through tube 44 into the mask 36 while the tube 46 which is the exhaust tube, is closed. As the pressure increases the mask 36 expands to the position shown in FIG. 2 wherein the internal surfaces and the stator are contacted by the mask 36 and are completely masked off thereby. In this position, therefore, no coating can be disposed upon the masked surfaces.

Attached to the lower portion of the annular housing 32 is a longitudinally extensible bellows 54 which is clamped onto the housing 32 at the upper end thereof and is clamped to a lower chamber housing portion 56 at the lower end thereof. The lower chamber housing 56 carries a foraminiferous screen 58 therein which is preferably made of porous metal having a porosity insufl'icient to permit the plastic powder used to sift therethrough. Beneath the screen 58 is an inlet 60 which supplies air or other gaseous medium under pressure to the chamber 62 beneath the screen 58. The air may be supplied from any suitable means such as a small compressor or agitator 64 mounted on the chamber wall 56. When the bellows 54 is in its expanded position as shown in FIG. 2 plastic powder held in a supply chamber 65 is metered into the chamber 30 above the screen 58 by means of a metering screw 68. The screw 68 is predeterminately controlled to supply the desired amount of powder upon each operation and is turned by a motor through gear reducing apparatus not shown. After the required amount of powder is supplied to the chamber 3t) and bellows 54, for example to the level shown in FIG. 2, the air compressor or agitator 64 is energized to supply air to the chamber. Thereafter the powder in the chamber will be fluidized and will rise to the level indicated by the dot and dash line noted at '70. The fluidizing bed is maintained and the lower chamber 36 is then caused to move upwardly by a piston rod 72 passing through plate 21 to collapse the bellows to the position shown in FIG. 5. In this position the top level of the cloud has moved from the dot dash line noted at 70 to-the dot dash line noted at 72 and has passed through the stator slots to a point above the stator. During thi entire procedure the stator is maintained completely stationary. The cloud is maintained in the upward position for a suitable length of time varying from seconds to a minute under normal conditions and the piston rod 72 is then caused to recede whereby the bellows 54 is elongated to its initial condition shown in FIG. 2. This causes the cloud of plastic particles to also recede and move away from the the stator. Thereafter air jets or blow offs 76 are activated to cause air to blow tangentially into the upper chamber 26. Simultaneously a suction device is activated to cause a suction to be present at the duct 88 which draws excess powder in the upper chamber 26 into the supply tank 66 whereit is bafiled and dropped by gravity into the main supply.

Thereafter the hydraulic inlet 44 is closed and exhaust 46 is opened to cause the mask 36 to deflate to the position shown in FIG. 1. The piston 24 is next activated to draw the upper chamber and attached mechanism to the starting position as shown in FIG. 1. The stator 34 now coated with plastic particles may be removed from its position on the chamber housing 32 and placed inan oven to homogenize the coating. An uncoated stator is then placed on the housing 32 and the operations just described are repeated. i

Itis apparent that all of the operations involving the feed screw 68, blower 64, water inlet 44 and exhaust 46, blow off operations for the blow olf jets 76 and draw olf operations through tube tit} may be suitably programmed by a suitable electrical interlock system if desired so that the operation is more or less automatic with the V exception of placement and removal of the stator, such automation being conventional in the art! It will be seen from the foregoing description that the stator may be coated with uniform coating while the' stator remains stationary at all times. This,"we believe, provides a more uniform thickness. coating thereover the surfaces of the stator. The use of the. blow ofls which may be present in any number, preferably four as shown, eliminates heavy coatings at the horizontal surfaces since the powder is removed almost immediately so that any excess powder does not adhere to the stator. Furthermore, since the coating operation is so well regulated there is less waste of powder due to non-uniformity of coating. The entire sequence of operations on a single stator may be accomplished in less than 30 seconds according to the temperature and powder being used.

Another advantage of the present apparatus and method concerns the step by step feeding of powder by the screw 68. The screw 68 replaces the quantity of powder used up after each coating operation whereby the density of the fluidized bed is maintained uniform at all times. This is of considerable importance to the satisfactory operation of the device since in past procedures the density of the fluidized bed gradually reduces as articles are coated since powder is only added thereto periodically while the inlet pressure of hydraulic fluid to maintain the bed in a fluidized condition is constant. This causes a non-uniformity of coating which is undesirable particularly where high edge strength and coverage are desired. This is particularly important in the case of an electrical core such as a stator wherein the insulation must be sufiicient to prevent the enamel coating of wires subsequently wound thereon from being cut or scraped.

It is apparent that modifications of present method and apparatus may be used to coat any article in a bed. It is not necessary that the mask be used if the article is to be coated all over and similarly if the external surfaces are to be coated the article may be held in spaced relation to the walls of the upper or lower chambers by means of a standard, hook, etc., as the case may be. In any instance, however, the coating operation is maintained by holding the article stationary and raising the fluidized bed to envelope the same wherein the fluidized bed is of constant density due to the replacement of plastic particles upon each operation thereof.

It will be noted in FIGS. 2 and 5 that a plate 90 is shown on top of the forarniniferou screen 58. This is used as a deflector directly beneath the inflatable mask 36. This causes a break down of the cloud or fluidized bed directly beneath the impervious surfaces of the mask and concentrates the fluidized particles at the outer periphery of the fluidizing chamber. It is apparent that this mask or plate 96 will be eliminated or changed in shape to conform to the part being coated to obtain best results.

A specific example of the materials, times and conditions required for coating a stator are set forth as follows:

'In the coating of the stator having an outside diameter of 5 /2" and an inner diameter of 3" with 12 slots and having a thickness of 2", 350 to 375 mesh epoxy powder is utilized wherein the stator is heated to a temperature of 375 F. After the bed is fluidized it is caused to pass through the stator as noted and then caused to recede. Performing the entire operation requires about 20 seconds wherein powder is in contact with the part about 6 seconds. During this period the epoxy powder adheres to the exposed surfaces of the stator in a layer of about .Ol2-.0l5 inch thick. The stator is initially heated as noted to a temperature of 375 F. and after the coating operation is immediately homogenized in an oven for 30 minutes at 400 F. It is apparent that the conditions set forth may vary within thelimits as is well known to persons skilled in the art. Similarly, other types of powder may be coated onto the stator or other'articles using proper temperature conditions for the specific powder wherein at times of immersion etc. are maintained subtantially the same for similar thickness coatings. It is understood that if the coating is to be thicker that slightly longer immersion will be used while if it is to be thinner the period of immersion is to be reduced. In

general, it is noted that the specific control factors for a specific article to be coated'are best determined by actual cloud of particles may be varied to obtain the results de sired.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. An apparatus for coating the surface of a hollow article with thermoplastic coating wherein the article is preheated to a temperature above the melting point of said thermoplastic coating comprising in combination; a closed chamber composed of a movable lower portion and a movable upper portion, said lower chamber portion comprising a surface adapted to receive and support the article to be coated, an inflatable masking means located within said upper chamber portion, means operable to move said movable upper chamber portion into engagement with and away from the hollow article to be coated when the article is supported by said lower chamber portion, a pressure fluid source and control means connected to said masking means whereby it is deflated and received within the hollow article when said movable upper chamber portion is brought into engagement with the article, a lower chamber housing member axially aligned with said lower chamber portion and connected thereto by a hollow flexible bellows means, a screen member in said lower chamber housing member to receive and support thermoplastic powder particles, means positioned to discharge pressurized gas beneath said screen and mix said thermoplastic powder particles in a fluid cloud which is not in contact with the hollow article, said masking means being inflated by said control means to engage and protect specified surfaces of the hollow article prior to formation of the fluid cloud, and means operable to raise said lower chamber housing whereby said cloud within said housing and said bellows is raised to contact the hollow article and coat desired surfaces thereof, said control means being actuated to deflate said masking means when the coating opertaion is completed and said upper chamber portion is moved away from the hollow article by its operating means.

2. An apparatus for coating the surface of a hollow article with a thermoplastic coating as described in claim 1 wherein a means is provided to dispense a predetermined quantity of thermoplastic powder particles into said lower compartment.

References (Iited by the Examiner UNITED STATES PATENTS 762,299 6/04 Fulton 222-206 1,854,458 4/32 Quincy et a1 222215 2,178,158 10/39 Aulbach 118421 X 2,600,253 1/52 Lutz.

2,815,550 12/57 Valyi 30229 X 2,844,489 7/58 Gemmer 1172l X 2,969,038 1/ 61 Neumann 118429 2,987,413 6/61 Dettling et al. 117-21 3,019,126 l/62 Bartholomew 117-17 3,028,266 4/62 Larsh 1l8504 X 3,074,808 1/ 63 Harrison 117-18 3,093,510 6/11 Olson et al. 118421 X FOREIGN PATENTS 1,051,175 2/59 Germany.

OTHER REFERENCES Kunststoife, vol. 47, No. 8, 1957, pp. 510, 511, and 512. Modern Plastics, October 1958, p. 125.

WILLIAM D. MARTIN, Primary Examiner.

RICHARD N. NEVIUS, J. REBOLD, Examiners. 

1. AN APPARATUS FOR COATING THE SURFACE OF A HOLLOW ARTICLE WITH THERMOPLASTIC COATING WHEREIN THE ARTICLE IS PREHEATED TO A TEMPERATURE ABOVE THE MELTING POINT OF SAID THERMOPLASTIC COATING COMPRISING IN COMBINATION; A CLOSED CHAMBER COMPOSED OF A MOVABLE LOWER PORTION AND A MOVABLE UPPER PORTION, SAID LOWER CHAMBER PORTION COMPRISING A SURFACE ADAPTED TO RECEIVE AND SUPPORT THE ARTICLE TO BE COATED, AN INFLATABLE MASKING MEANS LOCATED WITHIN SAID UPPER CHAMBER PORTION, MEANS OPERABLE TO MOVE SAID MOVABLE UPPER CHAMBER PORTION INTO ENGAGEMENT WITH AND AWAY FROM THE HOLLOW ARTICLE TO BE COATED WHEN THE ARTICLE IS SUPPORTED BY SAID LOWER CHAMBER PORTION, A PRESSURE FLUID SOURCE AND CONTROL MEANS CONNECTED TO SAID MASKING MEANS WHEREBY IT IS DEFLATED AND RECEIVED WITHIN THE HOLLOW ARTICLE WHEN SAID MOVABLE UPPER CHAMBER PORTION IS BROUGHT INTO ENGAGEMENT WITH THE ARTICLE, A LOWER CHAMBER HOUSING MEMBER AXIALLY ALIGNED WITH SAID LOWER CHAMBER PORTION AND CONNECTED THERETO BY A HOLLOW FLEXIBLE BELLOWS MEANS, A SCREEN MEMBER IN SAID LOWER CHAMBER HAVING MEMBER TO RECEIVE AND SUPPORT THERMOPLASTIC POWDER PARTICLES, MEANS POSITIONED TO DISCHARGE PRESSURIZED GAS BENEATH SAID SCREEN AND MIX SAID THERMOPLASTIC POWDER PARTICLES IN A FLUID CLOUD WHICH IS NOT IN CONTACT WITH THE HOLLOW ARTICLES, SAID MASKING MEANS BEING INFLATED BY SAID CONTROL MEANS TO ENGAGE AND PROTECT SPECIFIED SURFACES OF THE HOLLOW ARTICLE TO FORMATION OF THE FLUID CLOUD, AND MEANS OPERABLE TO RAISE SAID LOWER CHAMBER HOUSING WHEREBY SAID CLOUD WITHIN SAID HOUSING AND SAID BELLOWS IS RAISED TO CONTACT THE HOLLOW ARTICLE AND COAT DESIRED SURFACES THEREOF, SAID CONTROL MEANS BEING ACTUATED TO DEFLATE SURFACES THEREOF, SAID CONTROL THE COATING OPERATION IS COMPLATED AND SAID UPPER CHAMBER PORTION IS MOVED AWAY FROM THE HOLLOW ARTICLE BY ITS OPERATING MEANS. 